A 55-year-old woman presents to her family physician with a 1-week history of dizziness. She experiences spinning sensations whenever she lies down and these sensations increase when she turns her head to the right. These episodes are transient, intermittent, last for less than a minute, occur multiple times in a day, and are associated with nausea. Between the episodes, she is fine and is able to perform her routine activities. She denies fever, hearing disturbances, diplopia, tinnitus, and recent flu or viral illness. Past medical history is significant for diabetes mellitus type 2, hypertension, and hypercholesterolemia. She does not use tobacco or alcohol. Her blood pressure is 124/78 mm Hg, the heart rate is 79/min, and the respiratory rate is 13/min. During the examination, when she is asked to lie supine from a sitting position with her head rotated towards the right side at 45°, horizontal nystagmus is observed. What is the next best step in the management of this patient?

MRI of the brain with gadolinium

A 55-year-old woman presents to the physician with repeated episodes of dizziness for the last 3 months, which are triggered by rising from a supine position and by lying down. The episodes are sudden and usually last for less than 30 seconds. During the episode, she feels as if she is suddenly thrown into a rolling spin. She has no symptoms in the period between episodes. The patient denies having headaches, vomiting, deafness, ear discharge or ear pain. There is no history of a known medical disorder or prolonged consumption of a specific drug. The vital signs are within normal limits. On physical examination, when the physician asks the woman to turn her head 45° to the right, and then to rapidly move from the sitting to the supine position, self-limited rotatory nystagmus is observed following her return to the sitting position. The rest of the neurological examination is normal. Which of the following is the treatment of choice for the condition of this patient?

Oral prednisolone for 2 weeks and follow-up

Oral meclizine for 6 weeks and follow-up

A 23-year-old man presents to the emergency room following a stab wound to the back. He was in a bar when he got into an argument with another man who proceeded to stab him slightly right of the midline of his back. He is otherwise healthy and does not take any medications. He has one previous admission to the hospital for a stab wound to the leg from another bar fight 2 years ago. His temperature is 99°F (37.2°C), blood pressure is 115/80 mmHg, pulse is 100/min, and pulse oximetry is 99% on room air. Cardiopulmonary and abdominal exams are unremarkable; however, he has an abnormal neurologic exam. If this wound entered his spinal cord but did not cross the midline, which of the following would most likely be seen in this patient?

Ipsilateral flaccid paralysis at the level of the lesion

Contralateral spasticity below the level of the lesion

Ipsilateral loss of pain and temperature sensation below the lesion

Contralateral loss of tactile, vibration, and proprioception below the lesion

Contralateral loss of sensation at the level of the lesion

Descending motor pathways in brainstem for USMLE Step 1: High-Yield Anatomy Lessons

Corticospinal & Corticobulbar Tracts - The Voluntary Virtuosos

Origin: Primary motor cortex (precentral gyrus) & other frontal/parietal areas.
Function: Conscious, skilled voluntary movement.
- Corticospinal (Pyramidal) Tract: Controls contralateral body/limb muscles.
- Corticobulbar Tract: Controls contralateral head, face, & neck muscles via cranial nerves (V, VII, IX, X, XI, XII).

Corticospinal Tract: Origin, Path, and Decussation

⭐ Exam Favorite: A lesion in the posterior limb of the internal capsule can cause contralateral hemiparesis/hemiplegia, affecting the face, arm, and leg due to the dense packing of corticospinal and corticobulbar fibers.

Brainstem's Extrapyramidal Team - The Unconscious Movers

Function: Modulate involuntary motor control, including muscle tone, balance, posture, and reflexes.
**Posture & Balance Tracts (Antigravity Muscles):
- Vestibulospinal Tracts:
  - Origin: Vestibular nuclei (pons/medulla).
  - Action: Facilitates extensor tone (legs) & neck muscle activity to maintain balance in response to head movement.
- Reticulospinal Tracts:
  - Origin: Reticular formation.
  - Action: Pontine (medial) tract ↑ extensor tone; Medullary (lateral) tract inhibits it, providing fine-tuned postural adjustment.
Reflexive Movement & Coordination Tracts:
- Rubrospinal Tract:
  - Origin: Red Nucleus (midbrain).
  - Action: Facilitates flexor tone, primarily in the upper extremities.
- Tectospinal Tract:
  - Origin: Superior Colliculus (midbrain).
  - Action: Coordinates head & eye movements in response to visual/auditory stimuli.

Brainstem Descending Motor Pathways

⭐ Decerebrate Posturing: A lesion below the Red Nucleus causes unopposed activity of the Vestibulospinal and Pontine Reticulospinal tracts, leading to rigid extension of all four limbs.

Lesion Localization - Posture Puzzles

Decorticate (Flexor) Posturing
- Arms flexed or bent inward on the chest, hands clenched into fists, legs extended.
- Indicates lesion above the Red Nucleus (e.g., cerebral hemispheres, internal capsule).
- 📌 Mnemonic: "Hands to the core of the body."
Decerebrate (Extensor) Posturing
- Arms and legs extended, wrists flexed, neck arched.
- Indicates lesion below the Red Nucleus, transecting the brainstem.
- 📌 Mnemonic: "Lots of E's for Extensor."

Brainstem lesions and their effect on posture

⭐ Prognostic Pearl: Decerebrate posturing signifies more severe brainstem damage and carries a worse prognosis than decorticate posturing.

High‑Yield Points - ⚡ Biggest Takeaways

The corticospinal tract is the principal pathway for voluntary motor control, with fibers decussating at the pyramidal decussation.

The rubrospinal tract, from the red nucleus, primarily facilitates flexor muscles of the upper limbs.

Vestibulospinal tracts are crucial for maintaining balance and posture by activating antigravity (extensor) muscles.

Reticulospinal tracts from the reticular formation modulate muscle tone, posture, and crude voluntary movements.

The tectospinal tract coordinates reflexive head and neck movements in response to visual stimuli.

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